Lithotripters for extracorporeal disintegration of kidney stones are now well known, and are a welcome alternative to the surgery often previously needed for excision of kidney stones. Lithotripters generally comprise a truncated ellipsoidal reflector. An ellipsoid is a geometric body of revolution having two focus points. The reflector is truncated so that the second focus point lies a few inches from the physical end of the reflector. A rubber or the like diaphragm covers the otherwise open, truncated end of the reflector, and extends somewhat beyond that end. The reflector is filled with water. A spark gap is located at the first focus point which lies within the reflector. The reflector is positioned relative to a human body so that the second focus point lies on the kidney stone to be disintegrated. High voltage sparks pass between the electrodes and set up a shockwave. The shockwave is reflected and focused by the walls of the reflector, so that the shockwaves eventually coincide at the second focus point, and in due course reduce the kidney stone to a pile of small fragments that pass out with the urine.
The voltage that causes the sparks to jump across the gap is on the order of 12,000 to 20,000 volts. A typical treatment lasts from 40 minutes to one hour, and during that time the electrodes are essentially destroyed. As the electrodes wear down the gap between them increases somewhat, and the spark begins to deteriorate after a time, and with the deterioration of the spark the shockwaves also deteriorate, thereby rendering kidney stone disintegration less efficient. It is time-consuming and expensive to have to replace electrodes during a treatment, and yet this must from time to time be done.
Heretofore, it is has not been possible to accurately access the deterioration of the electrodes in a lithotripter, and therefore it has not been possible to determine at what point the electrodes should be replaced. This leads either to too frequent replacement of electrodes to be on the safe side, or alternatively, may lead to use of a pair of electrodes long after they have ceased to produce an efficient spark and resulting shockwave.